1. Field
Exemplary embodiments of the present invention relate to a light emitting diode and, more particularly, to a high efficiency GaN-based light emitting diode capable of preventing optical loss due to electrodes using a metamaterial.
2. Discussion of the Background
Generally, group-III nitrides, such as gallium nitride (GaN), aluminum nitride (AlN), and the like, have attracted attention as materials for light emitting diodes capable of emitting light in the visible and ultraviolet ranges due to excellent thermal stability and direct energy band gap. In particular, blue and green light emitting diodes using indium gallium nitride (InGaN) have been used in a wide range of fields, such as large color flat panel displays, signal lights, indoor lighting, high density light sources, high resolution output systems, optical communications, and the like.
Since it may be difficult to produce a homogeneous substrate capable of growing group-III nitride semiconductor layers, group-III nitride semiconductor layers may be grown on a heterogeneous substrate having a similar crystal structure through metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). A sapphire substrate having a hexagonal crystal structure may be used as a heterogeneous substrate. However, sapphire is an electrically non-conductive material, which may limit the structure of the light emitting diode. Accordingly, technology for fabricating a vertical-type high efficiency light emitting diode has been developed. In this technology, after epitaxial layers such as nitride semiconductor layers are grown on a heterogeneous substrate such as a sapphire substrate, a support substrate is bonded to the epitaxial layers, followed by separation of the heterogeneous substrate by laser lift-off or the like.
A metal substrate may be used as the support substrate in the vertical-type light emitting diode, thereby providing an excellent current spreading function in a vertical direction. In addition, after separation of the growth substrate, a roughened surface may be formed on an exposed N-plane of the gallium nitride layer through etching such as PEC, thereby providing excellent luminous efficacy.
However, since a vertical-type light emitting diode may include an N-electrode disposed on a light emitting surface, there may be a problem of optical loss due to the N-electrode absorbing or reflecting light generated in the light emitting diode, and preventing the light from being emitted to an outside of the light emitting diode. Although it may be necessary to reduce the area of the N-electrode in order to increase the area of the optical emitting surface, effective reduction in area of the N-electrode may be limited due to adhesive strength or current spreading requirements.
To solve such problems, a reflective metal layer may be disposed under the N-electrode to reflect light entering the N-electrode. However, as the reflected light is emitted to outside after passing through the epitaxial layers, there may be significant loss of light through the epitaxial layers.